1. Field of the Invention
Aspects of the present invention relate to a recording and/or reproducing method, a recording and/or reproducing apparatus, and an information storage medium therefor, and more particularly to a recording and/or reproducing method and a recording and/or reproducing apparatus to reduce a drop in data reliability or a reduction in data capacity due to different signal qualities of each layer of a multilayer information storage medium, and an information storage medium therefor.
2. Description of the Related Art
The development of high-capacity information storage media has resulted in active progress being made in the development of high-density multilayer information storage media. Discs of optical systems include cover layers in order to protect recording layers. The cover layers of multilayer discs are disposed between disc surfaces and recording layers. The thickness of cover layers of CDs, DVDs, and blu-ray DVDs (BDs) is 1.2 mm, 0.6 mm, and 0.1 mm, respectively. The greater the thickness of the cover layers, the higher the density of information that can be stored in the storage media. Cover layers of multilayer discs correspond to the multiple recording layers of the disc. The thicknesses of the cover layers vary according to a number of the recording layers. Therefore, a spot area where a light beam contacts a disc surface through an object lens varies according to a number of the recording layers. In 4, 8, and 16 multilayer discs, differences between minimum areas and maximum areas where the light beam contacts the disc surface must be increased. Therefore, the influence of dust particles on the light beam used to record and/or reproduce data to and or from the optical disc varies according to a number of recording layers. The degree of the variation is proportional to the number of recording layers. Thus, a method to overcome an error influence caused by dust, for each layer of multilayer discs, is needed.
FIG. 1 is a diagram to explain a difference in a spot area of each layer in accordance with different thicknesses of cover layers according to conventional technology. Referring to FIG. 1, since the thicknesses of cover layers vary according to a number of recording layers used in the disc, a spot area where a light beam contacts disc surfaces through an object lens varies according to a number of recording layers. That is, a spot area 2 of a cover layer 2 having a smaller thickness than a cover layer 1 is smaller than a spot area 1 of the cover layer 1, and the spot area 1 of the cover layer 1, which is a combination of the cover layer 2 and an additional cover layer between layer 2 and layer 1 and has a greater thickness than the cover layer 2, is greater than the spot area 2 of the cover layer 2. Thus, since a beam that is reflected by dust is blocked before reaching the target layer, the beam has a different degree of reflection by the dust according to a number of the recording layers. That is, the reflection amount of the beam is proportional to a “spot area”—an “area of the beam that is not incident/reflected by dust”. However, the “area of the beam that is not incident/reflected by dust” particles having the same size on a disc surface remains constant according to recording layers, whereas the “spot area” changes due to a different thickness of each cover layer according to recording layers.
Although a multilayer disc has a different error influence per layer due to a defect factor such as the same-sized dust particles, fingerprints, scratches, bubbles, and the like on the disc surface since cover layers have different thicknesses according to a number of recording layers, a conventional application of the same data format irrespective of a recording layer causes the following problem.
If a data format is based on a recording layer that is least influenced by a defect factor according to data capacity, data reliability is subject to a recording layer that is most influenced by the defect factor. Thus, a disc lifetime is reduced.
Furthermore, if the data format is based on the recording layer that is most influenced by the defect factor in order to compensate for the data reliability, the amount of additional information used to correct an error that occurs in a disc relatively increases, causing a reduction in the data capacity.
For example, in a four-layer disc, first and second layers have a similar error influence by a defect factor such as dust on the first and second layers, whereas third and fourth layers have a double error influence by the same defect factor as in the first and second layers. A data format suitable for the first and second layers causes a drop in data reliability of the third and fourth layers. A data format suitable for the third and fourth layers that are relatively vulnerable to the error influence causes an increase in additional information of the first and second layers, which reduces data capacity.
A data format is generally formed of user data and additional information. The user data is referred to as information that is to be substantially stored. The additional information is referred to as information, other than the information that is substantially stored, which is necessary for recording and the substantially stored information onto a disc or reproducing the substantially stored information. The user data is generally scrambled or modulated before being recorded/stored onto the disc. Examples of the additional information include sync information, address information, and parity information of a general optical system. The additional information according to an aspect of the present invention may hereinafter be referred to as the parity information.